The present disclosure relates generally to toners and toner processes, and more specifically, to toner compositions possessing excellent charging properties and dispensing performance.
Numerous processes are known for the preparation of toners, such as, for example, conventional processes wherein a resin is melt kneaded or extruded with a pigment, micronized, and pulverized to provide toner particles. Toner can also be produced by emulsion aggregation methods. Methods of preparing an emulsion aggregation (EA) type toner are within the purview of those skilled in the art, and toners may be formed by aggregating a colorant with a latex polymer formed by emulsion polymerization. For example, U.S. Pat. No. 5,853,943, the disclosure of which is hereby incorporated by reference in its entirety, is directed to a semi-continuous emulsion polymerization process for preparing a latex by first forming a seed polymer. Other examples of emulsion/aggregation/coalescing processes for the preparation of toners include those illustrated in U.S. Pat. Nos. 5,403,693, 5,418,108, 5,364,729, and 5,346,797, the disclosures of each of which are hereby incorporated by reference in their entirety. Other processes are disclosed in U.S. Pat. Nos. 5,527,658, 5,585,215, 5,650,255, 5,650,256 and 5,501,935, the disclosures of each of which are hereby incorporated by reference in their entirety.
Toner systems normally fall into two classes: two component systems, in which the developer material includes magnetic carrier granules having toner particles adhering triboelectrically thereto; and single component systems, which generally use only toner. Of the one-component development systems, both magnetic and non-magnetic systems are known. Magnetic systems involve the use of a toner containing a magnetic substance, which may preclude the development of sharp color images, which has led to a focus on non-magnetic systems.
The operating latitude of a powder electrophotographic development system may be determined to a great degree by the ease with which toner particles may be supplied to an electrostatic image. Placing charge on the particles, to enable movement and development of images via electric fields, is often accomplished with triboelectricity. Triboelectric charging may occur either by mixing the toner with larger carrier beads in a two component development (TCD) system, or by rubbing the toner between a blade and donor roll in a single component development (SCD) system.
With non-magnetic SCD, toner is supplied from a toner house to the supply roll and then to the development roll. The toner is charged while it passes a charging/metering blade. Non-magnetic SCD has been very popular for desk top color laser printers due to its compact size, since it does not need carrier in the development housing to charge toner. Non-magnetic SCD systems may thus utilize cartridges that are smaller in size compared with TCD systems, and the cost to a customer to replace a unit may, in some cases, be lower for a single component development system compared with a two component system.
There are several issues associated with SCD. The first is low charge and broad charge distribution on toner particles compared with conventional TCD toner. This is because the time for toner to flow through the gap between the blade and the development roll is very short. Low charge causes high background and low developability. Toner for SCD also has a high fines content, which may affect the charge and the print background. Also, the higher the fines content, the broader the charge distribution.
Another issue with SCD includes toner robustness in aging and in extreme environments such as A and C zone conditions found in an electrophotographic apparatus. The high stress under the blade may cause the toner to stick to the blade or the development roll. This may reduce the toner charge and the toner flowability. Since non-magnetic toner is charged through a charging/metering blade, low charging and low flowability can cause print defects such as ghosting, white bands, and low toner density on images.
Hence, toner compositions with excellent charging characteristics and excellent dispensing performance remain desirable.